The present invention relates to electrical test instruments and, in particular, to interconnections between test instruments and devices under test.
It has become common to perform multiple automatic tests in multiple regimes on semiconductor devices on a wafer, as well as at later points in a device's life, including in its final product.
Examples of common tests are IV measurements, CV measurements, general radio frequency (RF) measurements and vector network analyzers. Increasing, there is a demand for all of these tests to be not only as accurate as possible, but also to be performed as quickly and efficiently as possible. Unfortunately, besides the obvious differences in the test instrument configurations themselves used in the different tests, there also is presently a requirement to either change the cabling to the same test pins contacting the device under test (DUT) or to relocate the test connection using different pins.
In IV testing (a four-wire measurement), it is common to use two pairs of triaxial cables (each cable having an outer, intermediate and center connector) between the test instruments and two pins at the DUT. At the DUT (distal) end, the center conductors of a first pair of cables are connected to one pin and the center conductors of a second pair of cables is connected to the second pin. In general, the closer to the DUT that the conductors are connected together, the better, but mechanical constraints may force compromises. The two intermediate conductors of each pair are typically also connected together at the distal end. In operation, the intermediate conductors are then typically supplied with a guard voltage corresponding to the voltage on the respective center conductors. The outer conductors of the triaxial cables are typically just connected to a protective ground as the guard and center conductor voltages may be at a high potential. The test is basically DC and transmission line (distributed parameters) behavior is not typically a consideration.
In CV testing (a four-wire measurement), it is common to use two pairs of two-conductor coaxial cables between the test instruments and two pins at the DUT. At the distal end, the center conductors of a first pair of cables are connected to one pin and the center conductors of a second pair of cables is connected to the second pin. In general, the closer to the DUT that the conductors are connected together, the better, but mechanical constraints may force compromises. The outer conductors of the cables are typically connected to an instrument ground. This test is AC in nature, so transmission line (distributed parameters) behavior is typically a consideration. The two-conductor coaxial cables have a characteristic impedance, for example, 50 ohms. In addition, the test instruments and DUT terminations will typically have the same characteristic impedance.
In more general RF testing (a two-wire measurement), as well as vector network analyzers, it is common to use two two-conductor coaxial cables between the test instrument and two pins at the DUT. At the distal end, each center conductor is attached to a respective pin at the DUT. The outer conductors of the cable are typically connected to a ground. These tests are also AC in nature, so transmission line (distributed parameters) behavior is typically a consideration. The two-conductor coaxial cables have a characteristic impedance, for example, 50 ohms. In addition, the test instrument and DUT terminations will typically have the same characteristic impedance.
To perform the three types of tests above, it is typical to require three different cabling schemes as discussed above. Present solutions are to use different test pins for each test or to recable for each test. Using different test pins increases the number of operations needed for the tests and the time to perform the tests. In a further complication, it is possible to ameliorate some of the overhead required to recable by locating cable selecting switches near the DUT. This introduces additional mechanical constraints, measurement errors, calibration difficulties, costs and control issues.